1. Field of the Invention
The present invention relates to circuitry for generating ramp signals having controlled maximum amplitude. Preferred embodiments of the invention are circuits for generating multiple ramped voltage signals (for use in interleaved PWM dc/dc converters) such that the ramped voltage signals have constant phase shift and each ramped voltage signal has a controlled maximum amplitude.
2. Description of the Related Art
In power supply circuitry, it is often desired to produce multiple (parallel) channels of ramped voltages. For example, in some DC-DC converters (sometimes referred to as interleaved PWM DC/DC converters, where "PWM" denotes "pulse width modulated"), multiple channels of ramped voltages are provided to comparator circuitry for use in controlling the duty cycle of the DC-DC converter and thus the amplitude of the DC output voltage. The waveforms of the ramped voltages are identical (to the extent possible and practical) except that each has a different phase than the others. An advantage of providing multiple channels of ramped voltages of this type (rather than a single ramped voltage) is that use of multiple channels of ramped voltages allows the DC/DC converter with parallel power-processing channels to be implemented with smaller power stage inductors, smaller input filter inductors, and smaller output capacitors, thus providing an overall improved step-load transient response and reduced physical size.
More generally, circuitry providing multiple channels of ramped voltage signals (all the ramped signals being identical to the extent this can be achieved, except that each has a different phase) is useful for a wide variety of applications, including but not limited to interleaved PWM DC/DC converter applications. However, when implementing such circuitry (especially when implementing it as an integrated circuit or part of an integrated circuit), process and temperature variations typically cause variation from channel to channel in the characteristics (e.g., maximum amplitude) of the ramped voltages.